package org.apache.lucene.index;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

/**
 * TermDocs provides an interface for enumerating &lt;document, frequency&gt;
 * pairs for a term.
 * <p>
 * The document portion names each document containing the term. Documents are
 * indicated by number. The frequency portion gives the number of times the term
 * occurred in each document.
 * <p>
 * The pairs are ordered by document number.
 * 
 * @see IndexReader#termDocs()
 */

public interface TermDocs {
	/**
	 * Sets this to the data for a term. The enumeration is reset to the start
	 * of the data for this term.
	 */
	void seek(Term term) throws IOException;

	/**
	 * Sets this to the data for the current term in a {@link TermEnum}. This
	 * may be optimized in some implementations.
	 */
	void seek(TermEnum termEnum) throws IOException;

	/**
	 * Returns the current document number.
	 * <p>
	 * This is invalid until {@link #next()} is called for the first time.
	 */
	int doc();

	/**
	 * Returns the frequency of the term within the current document.
	 * <p>
	 * This is invalid until {@link #next()} is called for the first time.
	 */
	int freq();

	/**
	 * Moves to the next pair in the enumeration.
	 * <p>
	 * Returns true iff there is such a next pair in the enumeration.
	 */
	boolean next() throws IOException;

	/**
	 * Attempts to read multiple entries from the enumeration, up to length of
	 * <i>docs</i>. Document numbers are stored in <i>docs</i>, and term
	 * frequencies are stored in <i>freqs</i>. The <i>freqs</i> array must be
	 * as long as the <i>docs</i> array.
	 * 
	 * <p>
	 * Returns the number of entries read. Zero is only returned when the stream
	 * has been exhausted.
	 */
	int read(int[] docs, int[] freqs) throws IOException;

	/**
	 * Skips entries to the first beyond the current whose document number is
	 * greater than or equal to <i>target</i>.
	 * <p>
	 * Returns true iff there is such an entry.
	 * <p>
	 * Behaves as if written:
	 * 
	 * <pre>
	 * boolean skipTo(int target) {
	 * 	do {
	 * 		if (!next())
	 * 			return false;
	 * 	} while (target &gt; doc());
	 * 	return true;
	 * }
	 * </pre>
	 * 
	 * Some implementations are considerably more efficient than that.
	 */
	boolean skipTo(int target) throws IOException;

	/** Frees associated resources. */
	void close() throws IOException;
}
